Mobile machines, such as scrapers, dozers, motor graders, haul trucks, and wheel loaders often operate in extreme environments, where the machines encounter shock-loading and vibration introduced by the vehicle itself and by external inputs, such as uneven terrain at a worksite. Operators of the machines are exposed to these conditions, which can cause discomfort and increase a difficulty of controlling the machines. In order to improve operator comfort and machine control, machines sometimes employ suspension systems that help isolate the operator from machine movements.
Typical suspension systems include a spring to support the operator's seat, and a damper to control resonant motion of the seat. An exemplary suspension system is disclosed in U.S. Patent Publication 2010/0161182 of Contratto et al. that published on Jun. 24, 2010 (“the '182 publication”). In particular, the '182 publication discloses a vibration control system for a seat having a cylinder that is filled with air via an electromechanical valve. The cylinder is connected between the seat and a base that mounts to a floor of a machine cab. The vibration control system also includes a spring that couples the seat to the base. In response to an initial vibration, acceleration, or excursion of the seat caused by the associated machine or external input, movement of the valve is regulated to control an amount of air within the cylinder and thereby dampen displacement of the seat.
Although the control system of the '182 publication may help to isolate an operator from machine movement during normal operations through active dampening of a seat, it may still be less than optimal. In particular, the control system may not disclose any fail-safe functionality. That is, when power to the electromechanical valve is lost in conventional seat dampening systems, one of two things generally occurs. First, the electro-mechanical valve is completely opened such that the cylinder is rendered useless, thereby preventing any resonant cushioning to the operator. Alternatively, the electro-mechanical valve is completely closed such that the cylinder becomes sealed off from the environment, thereby making the seat completely rigid and providing no cushioning at all for the operator. The control system of the '182 does not describe a way of addressing these problems.
The present disclosure is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.